Monthly calendars are typically constructed with at least twelve sheets of paper with a single month in one particular year displayed on each sheet. Because the first weekday in each month varies monthly and yearly, each sheet of such a calendar is typically obsolete after the particular month has ended, and a user must display a separate sheet to accurately convey the current month. Likewise, an entire calendar is typically obsolete after the particular year has ended, and a user must discard the entire calendar and replace it with a calendar displaying the accurate configuration of days for the current year.
To counter this problem, several “perpetual calendars” have been invented that allow a single calendar to be reused to display multiple months of multiple years with the appropriate starting weekday.
One such calendar is described in U.S. Pat. No. 1,042,337 to Gorin. In this patent, a web or ribbon is horizontally movable behind an opaque glass front. The web or ribbon includes dates of a month arranged in columns or series so that when it is horizontally displaced, an opening in the glass front exposes the consecutive numbers 1-31 beginning on any weekday of the month. When the month has ended, a button of the last day of the month is pressed, and the web or ribbon is displaced to expose the days of the next month as beginning on the day after the weekday of the button pressed.
Although this perpetual calendar allows for a different starting day of each month, the user must read an alternate dial showing the usual number of days in the past month and press the relevant button to change the arrangement of days. This perpetual calendar also displays thirty-one days for every month, regardless of whether the month includes 28, 29, 30 or 31 days. This calendar also includes bulky and expensive mechanisms for translating the motion of the button to the change of the month and day configuration, such that if the user presses the wrong button, the user must recalculate the last day of the month and continue pressing that button until the proper month is again displayed.
Another perpetual calendar is described in U.S. Pat. No. 1,459,236 to Orth. This patent describes a perpetual calendar with adjustable knobs for the year, month and first day of the week for a given month. The knob for the first day of the week operates by horizontally displacing a web similarly to Gorin's perpetual calendar described above, but serves to display dates only for the upper four weeks of a current month. When turned, a fourth knob vertically displaces a second web to display one of twenty-one horizontal lines representing each of the possible date configurations of the last two weeks of a month. Although the Orth calendar therefore allows a user to display only the existing days for a month, including a leap year in February, a user must continue turning this fourth knob through many horizontal lines until the accurate number and configuration of days appear for the latter two weeks.
In a conventional calendar, a user may write notes directly onto the calendar pages to ensure that events, such as birthdays or meetings, are remembered on the correct day. Because the month page in a conventional calendar is obsolete at the month's end, the page can merely be torn off and thrown away. Because the month grid is reused in the perpetual calendars discussed above, any markings on the grid would be carried on to every month, causing confusion and inaccuracy.
Accordingly, a need exists for a perpetual monthly calendar that addresses one or more of these problems, allowing for an easier operation, write-on capability and/or simpler construction. Other objects, advantages, features and results will more fully appear in the course of the following description.